The opening operation in vacuum switches is initiated by the separation of the interacting contacts. During this process, there arises a metal vapor arc having foot points which should be put into motion to limit the burning of the contact pieces. In known contacts, this is accomplished by separate arc contact surfaces which surround the actual contact surfaces and which may be provided with slots to form guiding edges for the arc foot points. The contact pieces may then be constructed so that a rotation of the switching arc about the axis of the contact arrangement results.
Until now, efforts were directed to bringing about a radial expansion of the arcs by the utilization of loop forces. For example, the U.S. Pat. No. 3,211,866 describes a contact arrangement wherein concentric contact pieces are opened successively to increase the current loop. Such measures, however, may lead to the arcs leaving the area between the contacts and making contact with the vapor shields surrounding the contact arrangement. This may not only damage the vapor shields, but may also reduce the overall circuit-breaking capacity of the vacuum switch.